The Russians and the Ukrainians - What's the Biggest Blunder?

The russians have pulled back most of their best forces away from he north and the dan bas to reinforce the south. They re deployed im there, leaving it largely open. And they actually did not deploy any substantial amount of forces to try to cover this flank. Most of the units that appeared to have been there was a fairly thin force of rosguardia and mobilized elenar personnel.